Turbo Wheel And Shaft Assembly

ABSTRACT

A turbine wheel and shaft assembly is provided for a turbocharger including a turbine wheel including a body portion supporting a plurality of blades on a first axial face thereof. A hub extends from a body portion on a second axial face. A shaft is welded to the hub at a weld location spaced from the second axial face. The weld location is spaced axially from the second axial face by a distance sufficient to provide a significant reduction in the residual stresses in the welded parts. This design is intended to mitigate turbine wheel imbalance problems.

FIELD

The present disclosure relates to a turbocharger for engines, and more particularly, to a turbo wheel and shaft assembly for improved turbocharger performance.

BACKGROUND AND SUMMARY

This section provides background information related to the present disclosure which is not necessarily prior art.

Turbo charged engines utilize compressed air which results in a larger quantity of air being forced into the engine, creating more power. The energy used to drive the turbo compressor is extracted from waste exhaust gases. As the exhaust gases leave the engine, they are directed through a turbine wheel placed in the exhaust flow. The gases drive the turbine wheel, which is directly connected via a shaft to a compressor wheel. Increased exhaust gas flow drives the turbine wheel faster, providing the engine more air, thereby producing more power. Therefore, the turbocharger uses the extraction of energy from the exhaust gas to improve the engine efficiency.

Turbochargers are usually seen as power enhancement on performance cars, but today, turbochargers are becoming more regularly used to provide greater torque on small capacity engines. The advantages of using a turbocharged engine include improved fuel efficiency and reduced exhaust emissions. The components of the turbocharger generally include a housing defining a compressor chamber and a turbine chamber, a compressor wheel is disposed in the compressor chamber, and a turbine wheel is disposed in the turbine chamber. A turbine shaft is provided for connecting between the turbine wheel and the compressor wheel.

With reference to FIG. 4, a conventional turbine wheel and shaft assembly is shown wherein the turbine wheel includes a body portion 110 having a plurality of veins 112 extending from a first axial face thereof. A turbine shaft 114 is welded to the back surface of the turbine wheel body 110 at a weld location 118. A problem with current turbine wheel and shaft assemblies can be the imbalance of a turbine wheel that can cause noise and customer complaints. To address the problem of turbine wheel imbalance, turbine wheels and shaft assemblies are commonly balanced after the weld process is completed by rotating the assembly on a balancing machine which identifies the imbalances that can be corrected by removing material at different locations on the turbine wheel in order to obtain a balanced turbine wheel and shaft assembly.

It has been a discovery of the present invention, however, that as the seam between the turbine wheel and turbine shaft is welded, residual stresses are formed in the turbine wheel and shaft. These residual stresses are directly related to the heat put into the components during the welding process. The weld operation is performed utilizing a focused beam such as via electron beam welding, although laser welding or friction welding could also be used. After the weld process is completed, a defocused beam can be utilized to broaden the heating operation to relieve some of the residual stresses imparted to the turbine wheel and shaft. However, the turbine wheels and shaft assemblies that have been properly balanced after the welding process are placed in use in a turbocharger in which the temperatures can exceed 600° C. The heating of the turbine wheel and shaft assembly can cause the residual stresses from the welding process to relax that can result in wheel distortion. According to the theory of the discovery of the present application, because the weld location 118 is so close to the turbine wheel, a large amount of heat is required to adequately relieve the residual stresses in the large mass of the turbine wheel.

Accordingly, it is the intent of the present application to move the weld location further away from the mass of the turbine wheel body so that the weld is moved away from the large mass of the turbine wheel and a defocused beam can more easily relieve the residual stresses in the weld location. In addition, by moving the weld location away from the body of the turbine wheel, the weld can be placed in a lower operation temperature location to minimize the effects of weld residual stress relaxation on the wheel imbalance mitigation. Accordingly, the present disclosure provides a turbine wheel and shaft assembly for a turbocharger including a turbine wheel including a body portion supporting a plurality of blades on a first axial face thereof. A hub extends from the body portion on the second axial face. The hub has a predetermined diameter and a length. A shaft is welded to the hub at a weld location spaced from the axial face. The weld location is spaced axially from the second axial face of the body portion by a distance that is at least 50 percent, and more preferably, at least 75 percent of the diameter of the hub.

Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.

FIG. 1 is a schematic view of an engine utilizing a turbocharger, according to the principles of the present disclosure;

FIG. 2 is a cross-sectional view of a turbine wheel and shaft assembly according to the principles of the present disclosure;

FIG. 3 is a cross-sectional view of a turbine wheel and shaft assembly according to an alternative embodiment of the present disclosure; and

FIG. 4 is a cross-sectional view of a prior art turbine wheel and shaft assembly.

Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.

DETAILED DESCRIPTION

Example embodiments will now be described more fully with reference to the accompanying drawings.

Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed.

When an element or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

With reference to FIG. 1, a schematic view of a turbocharged engine according to the principles of the present disclosure will now be described. The engine 10 includes an engine structure 12 having a cylinder 14 therein. A piston 16 is provided within the cylinder 14 and is connected to a crankshaft 18 as is known in the art. The cylinder 14 defines a combustion chamber 20 that is in communication with an intake port 22, an exhaust port 24, and a fuel injector 26. The intake port 22 receives a compressed air flow 30 from a compressor 32 of a turbocharger 34. The exhaust port 24 is in communication with an engine exhaust gas flow passage 36 which is in communication with a turbine 38 of the turbocharger 34. As the engine exhaust gas flow 36 passes through the turbine 38, a turbine wheel 40 is caused to rotate within a turbine housing 42 and drives a turbine shaft 44 which is connected to a compressor wheel 46 of the compressor 32. Therefore, the exhaust gas flow 36 causes rotation of the turbo charger turbine wheel 40 and compressor wheel 46 which then compresses the intake air 48 that is delivered to the air intake 22 of the engine. A compressed air cooler 49 can cool the compressed air delivered to the air intake 22 and can include a fan 50.

According to the principles of the present disclosure, the turbine wheel 40 and shaft 44 are assembled in a unique manner that eliminates the imbalance problem of welded turbo wheel and shaft assemblies. In particular, as shown in FIG. 2, the turbine wheel 40 includes a body portion 52 that supports a plurality of blades 54 on a first axial face 56 thereof. A hub 58 extends from the body portion 52 on the second axial face 60. The hub 58 has a predetermined diameter D. The shaft 44 is welded to the hub 58 at a weld location 62 that is spaced from the second axial face 60 by a distance d_(w). According to a preferred aspect of the present disclosure, the weld location 62 is spaced axially from the second axial face by a distance d_(w) that is at least 50 percent, and more preferably, at least 75 percent of the diameter D of the hub 58. With this preferred weld distance spaced from the body portion 52 of the turbine wheel 40, the weld location 62 is moved away from the large mass portion of the body 52 so that less heat is put into the parts and, therefore, less residual stress is created. Furthermore, when the weld area is heated with a defocused beam, stress relief in the smaller mass regions surrounding the weld location 62 are more effective at relieving the residual stresses that had been created during the welding process. Furthermore, the weld location 62 being spaced a distance d_(w) away from the body 52 of the turbine wheel moves the weld location 62 to a lower operation temperature location within the turbocharger 34 to minimize the effects of weld residual stress relaxation on the wheel imbalance mitigation. There is typically a piston ring seal located adjacent to the current practice weld location that prevents oil from exiting the bearing housing. Moving the weld location to position 62 locates the weld on the oil wetted side of the piston ring seal 63 (shown schematically in FIG. 1), thereby placing the welded location 62 in a significantly cooler location.

To further reduce the residual stresses, it is advantageous to also reduce the mass of the shaft 44 by providing a hollow cylindrical shaft. In addition, the hub 58 can also be hollowed out in order to reduce the mass in the weld region to thereby eliminate distortion of the parts. It is noted that the removal of the additional mass by providing a hollow shaft 44 and a hollow region within the hub 58 is optional, although it can increase the cooling rates of the parts while also reducing the residual stresses that are generated during the welding process. In the embodiment shown in FIG. 2, the shaft 44 is provided with an annular flange portion 64 at its end where it is welded to the hub portion 58 of the turbine wheel 40. The weld location 62 is provided at the interface between the flange 64 and the hub 58 as illustrated.

According to an alternative embodiment as illustrated in FIG. 3, the weld location 62′ can be provided between the hub portion 58 and the unflanged end of the shaft 44′. It is noted that at this location, the weld diameter can be reduced to the diameter of the shaft 44′ so that less circumferential area of welding is required thereby providing less residual stress in the resultant welded parts. It is noted that the amount of hollow region within the hub 58 can be extended into the body portion 52 of the turbine wheel 40. With these additional modifications, the turbine wheel and shaft weight can be reduced thereby further reducing the turbo wheel inertia and to provide wheel imbalance mitigation. According to the principles of the present disclosure, the imbalance induced noise issues can be eliminated or significantly reduced by the proposed design configurations thereby significantly improving part quality and performance.

The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure. 

What is claimed is:
 1. A turbine wheel and shaft assembly for a turbocharger, comprising: a turbine wheel including a body portion supporting a plurality of blades on a first axial face thereof and a hub extending from said body portion on a second axial face, said hub having a diameter; a shaft welded to said hub at a weld location spaced from said second axial face, wherein said weld location is spaced axially from said second axial face of said body portion by a distance that is at least 50 percent of said diameter.
 2. The turbine wheel and shaft assembly according to claim 1, wherein said shaft includes a cylindrical body and a radially extending flange portion at an end thereof that is welded to said hub of said turbine wheel.
 3. The turbine wheel and shaft assembly according to claim 1, wherein said shaft is hollow.
 4. The turbine wheel and shaft assembly according to claim 1, wherein said hub includes a hollow portion therein.
 5. A turbocharger, comprising: a housing including an inlet for receiving an engine exhaust gas flow, a turbine chamber and an outlet for exhaust gas discharge; a turbine wheel and shaft assembly disposed in said turbine chamber and including a turbine wheel having a body portion supporting a plurality of blades on a first axial face thereof and a hub extending from said body portion on a second axial face opposite the first axial face, said hub having a diameter, and a shaft having a first end welded to said hub at a weld location spaced from said second axial face, wherein said weld location is spaced axially from said second axial face of said body portion by a distance that is at least 50 percent of said diameter.
 6. The turbocharger according to claim 5, wherein said shaft includes a cylindrical body and a radially extending flange portion at the first end thereof that is welded to said hub of said turbine wheel.
 7. The turbocharger according to claim 5, wherein said shaft is hollow.
 8. The turbo charger according to claim 5, wherein said hub includes a hollow portion therein.
 9. The turbo charger according to claim 5, further comprising a compressor wheel attached to a second end of said shaft and disposed in a compressor chamber.
 10. The turbo charger according to claim 5, further comprising a seal disposed between said second axial face of said turbine wheel and said weld location.
 11. An engine, comprising: an engine structure defining a plurality of cylinders receiving a respective piston therein and having inlet and exhaust passages in communication with each of the cylinders; a turbocharger comprising: a housing including an inlet for receiving an engine exhaust gas flow from said exhaust passages, a turbine chamber and an outlet for exhaust gas discharge; a turbine wheel and shaft assembly disposed in said turbine chamber and including a turbine wheel having a body portion supporting a plurality of blades on a first axial face thereof and a hub extending from said body portion on a second axial face opposite the first axial face, said hub having a diameter, and a shaft welded to said hub at a weld location spaced from said second axial face, wherein said weld location is spaced axially from said second axial face of said body portion by a distance that is at least 50 percent of said diameter.
 12. The engine according to claim 11, wherein said shaft includes a cylindrical body and a radially extending flange portion at an end thereof that is welded to said hub of said turbine wheel.
 13. The engine according to claim 11, wherein said shaft is hollow.
 14. The engine according to claim 11, wherein said hub includes a hollow portion therein.
 15. The engine according to claim 11, further comprising a compressor wheel attached to a second end of said shaft and disposed in a compressor chamber.
 16. The engine according to claim 15, wherein said compressor chamber is in communication with an air inlet and a compressed air outlet that is in communication with said inlet passages of said cylinders.
 17. The engine according to claim 11, further comprising a seal disposed between said second axial face of said turbine wheel and said weld location. 